The Finder icon on the dock is the two-colored smiley face. It has been there for ages and it's come to be the face of OS X. But did you know that you can actually change it to something else? You can customize the Finder icon to your liking.
Arguably, Mac OS X doesn't let you customize it easily. There are no preferences that you can use to tweak it. It's a little tough (involving terminal commands and copy-pasting) but it's not complicated. Check it out.
Here is How to Change the Finder Dock Icon in Mac OS X:
Step 1: Make a PNG file of the icon you want to replace the Finder icon with. Non-retina Mac users: save it as finder.png and Retina Mac users: save it as firstname.lastname@example.org
Step 3: Open Finder from dock or from the menu bar. Press Command + Shift + G to launch the ‘Go to Folder.’
Step 4: Type this:
Step 5: Now search for the file named finder.png or email@example.com. Copy the file to your desktop (this is a backup for safety).
Step 6: In the “Resource” folder, drag the new icon (finder.png) you want to use. Click on Replace if you are asked if you want to replace the existing finder.png file with the new one.
Step 7: Once again press Command + Shift + G. Then, type:
Step 8: Type “com.apple.dock.iconcache” in the search box. Click on the “folders” tab to search within this folder.
Step 9: Delete the “com.apple.dock.iconcache” file.
Step 10: Launch Terminal from Application > Utilities and type:
Step 11: Your dock will be refreshed and your Finder icon will change to the new one.